Soil and crop management under conservation agriculture in Zimbabwe
To Our Readers
The end of 2009 is fast approaching. I would like to thank you all for the support that you have provided in your role within coordinated research projects (CRPs) or as a counterpart in technical cooperation projects (TCPs). I am also indebted to research institutions and local scientists who have provided vital support to the successful im- plementation of the research coordinated meeting (RCM) on managing irrigation wa- ter in China. Without your support and commitment, we would not be able to accom- plish all the objectives outlined in our CRPs and TCPs for 2009. In this Newsletter, you will find interesting information on some of the activities that you and the Soil and Water Management & Crop Nutrition (SWMCN) Subprogramme have engaged in during the course of 2009 to address land and water management issues for food security and environmental sustainability.
With your continuing support and commitment, the SWMCN Subprogramme is looking forward to meeting new challenges in 2010. One of these challenges will be a development of new initiatives on soil and water management practices with the aim of providing not only sustainable food production but also enhancing soil carbon sequestration and minimizing emissions of greenhouse gases (GHG) such as carbon dioxide, nitrous oxide and methane. Two new coordinated research projects will be initiated in 2010 to investigate the impacts of mulch and non mulch and soil man- agement on soil carbon sequestration, GHG emissions and soil quality. Another chal- lenge is to enhance the successful outcomes of our activities in Member States.
Vol. 32, No. 2 January 2010
http://www-naweb.iaea.org/nafa/index.html ISSN 1011-2650
http://www.fao.org/ag/portal/index_en.html
Contents
• To Our Readers 1
• Staff 4
• Staff News 5
• Feature Articles 5
• SWMCN Seminar
Series 13
• Technical Cooperation
Projects 15
• Forthcoming Events 18
• Past Events 19
• New Coordinated Research Projects
(CRPs) 24
• Status of Coordinated Research Projects
(CRPs) 24
• Activities of the Soil Science Unit 27
• Publications 37
Your active involvement in the dissemination of informa- tion to farming communities and policy makers will go a long way towards ensuring the adoption and sustainabil- ity of our collective results.
The activities of the SWMCN Subprogramme in soil and water management and crop nutrition are increasingly important not only to ensure land productivity for food security, but also to enhance soil resilience against the impacts of climate change and variability on soil erosion and degradation. This view is consistent with the increas- ing emphasis expressed by the international scientific and policy communities through various forums on the im- portant role of sustainable land (soil and water) manage- ment for climate mitigation and adaptation. Examples in- clude the Land Day organized by the UN Convention to Combat Desertification (UNCCD) on 6 June 2009 and the Copenhagen FAO Side Event on Climate Change and Food Security (10 December 2009). The SWMCN Sub- programme will need your full help and support to ad- dress sustainable land management for climate change and mitigation.
The year 2009 has brought both good and sad news for the SWMCN Subprogramme. The passing of Dr. Jerry Richie in June came as a big shock to all of us in the SWMCN Subprogramme. Jerry had been a key member of our coordinated research networks on the use of fallout radionuclides as tracers to measure soil erosion- sedimentation patterns across agricultural landscapes and also to assess the impacts of various conservation meas- ures and land use practices on mitigating soil erosion and improving water quality in lakes, reservoirs and flood- plains. We treasured his friendship, understanding and support to all team members within the CRPs that Jerry has been involved with and I am grateful that I had the opportunity to work with Jerry. We would like to extend our sincere condolences to Jerry’s family and colleagues at the Agricultural Research Service, U.S. Department of Agriculture (USDA), Beltsville in their sad loss.
In November, I received the good news from Lancaster University that Professor William Davies and his team at the Lancaster Environment Centre, United Kingdom re- ceived a Queen’s Anniversary Prize for Higher and Fur- ther Education Award for their work on soil-microbe- plant interactions and plant stress signalling with the ul- timate aim of economically viable crop yields under wa- ter limiting conditions. This work which has been carried out as part of an IAEA- funded technical contract shows how the signals at roots in drying soils send to the shoots can help plants cope more successfully with drought and produce better yield. Our warmest Congratulations to you, William.
In celebrating the successful implementation of our ac-
both in the SWMCN Section and the SSU for their inputs and commitment. The support of the SSU in fellowship training, analytical support to CRPs and research and de- velopment is critical to the successful achievements of the SWMCN Subprogramme. Last but not least my thanks to the Director and colleagues of the Joint FAO/IAEA Programme of Nuclear Techniques in Food and Agriculture Programme and Division for their sup- port of the SWMCN Subprogramme. I wish you all good health and a very successful 2010.
Long Nguyen Head Soil and Water Management and
Crop Nutrition Section
Soil and Water Management & Crop Nutrition Subprogramme
L. Nguyen L. Heng G. Dercon K. Sakadevan
G. Hardarson J. Adu-Gyamfi L. Mabit P. Macaigne
L. Mayr J. Luis Arrillaga M. Aigner M. Heiling
R. Hood A. Toloza P. Jankong S. Linic
R. Leon de Müllner B. Liepold E. Swoboda N. Jagoditsch
Staff
Joint FAO/IAEA Programme of Nuclear Techniques in Food and Agriculture, Vienna International Centre, Wagramer Strasse 5, P.O. Box 100, A-1400 Vienna, Austria;
Telephone (43-1) 2600 + ext.; Fax (43-1) 2600 7; E-mail: Official.Mail@iaea.org
Name Title E-Mail Address Extension
Qu LIANG Director Q.Liang@iaea.org 21610
Soil and Water Management and Crop Nutrition Section
Name Title E-Mail Address Extension
Long NGUYEN Section Head M.Nguyen@iaea.org 21648
Lee Kheng HENG Technical Officer L.Heng@iaea.org 26847
Gerd DERCON Technical Officer G.Dercon@iaea.org 21693
Karuppan SAKADEVAN Technical Officer K.Sakadevan@iaea.org 21613
Peggy MACAIGNE Consultant P.Macaigne@iaea.org 26843
Rosario LEON DE
MÜLLNER Secretary R.Leon-De-Muellner@iaea.org 21647
Brigitte LIEPOLD Clerk B.Liepold@iaea.org 21646
FAO/IAEA Agriculture and Biotechnology Laboratory, A-2444 Seibersdorf, Austria
Name Title E-Mail Address Extension
Qu LIANG Acting Head, FAO/IAEA Agricul-
ture and Biotechnology Labora- tory
Q.Liang@iaea.org 21610
Soil Science Unit
Name Title E-Mail Address Extension
Gudni HARDARSON Unit Head G.Hardarson@iaea.org 28277
Joseph ADU-GYAMFI Soil Scientist/Plant Nutritionist J.Adu-Gyamfi@iaea.org 28263
Lionel MABIT Soil Scientist L.Mabit@iaea.org 28271
Sasa LINIC Consultant S.Linic@iaea.org 28263
Leopold MAYR Senior Laboratory Technician L.Mayr@iaea.org 28305
José Luis ARRILLAGA Senior Laboratory Technician J.L.Arrillaga@iaea.org 28306 Martina AIGNER Senior Laboratory Technician M.Aigner@iaea.org 28212 Maria HEILING Senior Laboratory Technician M.Heiling@iaea.org 28272
Arsenio TOLOZA Laboratory Technician A.Toloza@iaea.org 28403
Norbert JAGODITSCH Laboratory Assistant N.Jagoditsch@iaea.org 28422
Elisabeth SWOBODA Secretary E.Swoboda@iaea.org 28362
Staff News
Ms. Patcharin Jankong joined the Soil Science Unit, FAO/IAEA Agriculture and Biotechnology Laboratory, Seibersdorf on 22 June 2009 as an intern from Thailand under the supervision of Lionel Mabit. Patcharin will be associated with field research investigations, laboratory work, research data analysis and publications related to the use of Fallout Radionuclides (FRNs) for soil erosion and sedimentation investigation in support of the SWMCN Subprogramme activities. Patcharin’s previous work and study include environmental research issues fo- cusing on pollutants analysis in the environment (e.g.
soil, water, plants and fish) and soil remediation (espe- cially the effect of rhizosphere factors such as fertilizer, bacteria, and mycorrhiza on soil phytoremediation) which she had conducted during her PhD studies at Mahidol University, Bangkok (Thailand) in collaboration with Karl-Franzen University, Graz (Austria).
Mr. Moncef Benmansour, from the Centre National de l’Energie des Sciences et des Technique Nucléaires (CNESTEN), Rabat, Morocco, joined the Soil Science Unit as a consultant for 2.5 months from 06 July to 11 September 2009. He has extensive expertise in radiomet- ric techniques, in the use of nuclear techniques in the en- vironment and agriculture fields and has participated in many IAEA projects (e.g. Regional TC projects and CRPs). During his period in IAEA, Moncef has been working with Lionel Mabit in Seibersdorf in soil subpro- gramme activities for producing a manual entitled ‘‘Soil erosion assessment using nuclear techniques’ for IAEA Member States on the use of fallout radionuclides (FRN) to investigate soil erosion and sedimentation processes. It is proposed to publish the manual as part of an IAEA Training Course Series.
Mr. Sasa Linic joined the Soil Science Unit on 8 June 2009 as a Consultant. Sasa has a Master Degree in Envi- ronmental Science (Natural Resource Management and Ecological Engineering) from University of Natural and Applied Life Sciences (BOKU), Austria and Lincoln University, New Zealand. Sasa will work with Joseph Adu-Gyamfi in the area of soil-water-plant relationship with a major focus on mechanisms of tolerance of crops to abiotic stress and crop-water productivity using iso- topic tracers (13C, 18O and 2H) and also provide support to the CRP on ‘Managing irrigation water to enhance crop productivity under water limited conditions using nuclear techniques’.
Ms. Rebecca Hood joined the SWMCN Subprogramme in January 2009 as a consultant on a part time basis. Hav- ing left the Soil Science Unit in 2004, Rebecca went on to organise the Joint European Stable Isotope Users group Meeting (JESIUM 2004) in Vienna, after which she re-joined FAO-IAEA, this time in the Entomology Unit where she applied her stable isotope expertise to in- sects. This fruitful collaboration resulted in numerous publications in the fields of mosquitoes, fruit flies and tsetse and culminated in a manual on the Use of Stable Isotopes in Entomology. After the birth of her second child in 2006 Rebecca returned to work on the Nitroge- nome Project at the University of Vienna which at- tempted to link microbial function to soil nitrogen proc- esses. She currently works on developing methods for measuring greenhouse gas emissions and carbon seques- tration. In addition she has been working on numerous ar- ticles and outreach materials for eventual publication.
Feature Articles
Nutrient balances in African land use systems across different spatial scales: a review of approaches, challenges and progress
J.G. Cobo1,2,G. Dercon3, G. Cadisch1
1 University of Hohenheim, Institute of Plant Production and Agroecology in the Tropics and Subtropics, 380a, 70593 Stuttgart, Germany
2 Tropical Soil Biology and Fertility Institute of the International Center for Tropical Agriculture (TSBF-CIAT), MP 228, Harare, Zimbabwe
3 Soil and Water Management and Crop Nutrition Subprogramme, Joint FAO/IAEA Division of Nuclear Techniques in Food and Agriculture, Department of Nuclear Sciences and Applications, International Atomic Energy Agency – IAEA, Vienna International Centre, P.O. Box 100,
1400, Vienna, Austria
Nutrient balances are useful tools as indicators of poten- tial land degradation and for optimizing nutrient use, and are thus highly relevant in the African context. A com- prehensive literature review on nutrient balances in Af- rica was carried out to illustrate the main approaches, challenges, and progress, with emphasis on issues of scale. The review showed nutrient balances being widely
used across the continent. The collected dataset from 57 peer-reviewed studies indicated however, that most of the balances were calculated at plot and farm scale, and gen- erated in East-Africa. Data confirmed the expected trend of negative balances in the continent for nitrogen and po- tassium, where >75% of selected studies had mean values below zero. For phosphorus, only 56% of studies showed
negative mean balances. Several cases with positive nu- trient balances indicated that soil nutrient mining cannot be generalized across the continent. Land use systems of wealthier farmers mostly presented higher nitrogen and phosphorus balances than systems of poorer farmers (p<0.001). Usually plots located close to homesteads also presented higher balances than plots located further away (p<0.05). Partial nutrient balances were significantly higher (p<0.001) than full balances calculated for the same systems, but the later carried more uncertainties. A change in the magnitude of nutrient balances from plot to continental level did not show any noticeable trend which challenges prevailing assumptions that an increasing trend exists. However, methodological differences made a proper inter-scale comparison of results difficult. The review illustrated the high diversity of methods used to calculate nutrient balances and highlighted the main pit- falls, especially when nutrient flows and balances were scaled-up. Major generic problems were the arbitrary in- clusion/exclusion of flows from the calculations, short evaluation periods and difficulties in setting spatial- temporal boundaries, inclusion of lateral flows and link-
ing the balances to soil nutrient stocks. A need to prop- erly describe the methods used and to report the estimates (i.e. using appropriate units and measuring variability and error) were also highlighted. The main challenges during scaling-up were related to the type of aggregation and in- ternalization of nutrient flows, as well as issues of non- linearity and spatial variability, resolution and extent, which have not yet been properly addressed. In fact, gathered information showed that despite a few initia- tives, scaling-up methods are still incipient. Lastly, prom- ising technologies and recommendations to deal with these challenges were presented to assist in future re- search on nutrient balances at different spatial scales in Africa and worldwide.
For further details refer to the following article:
J.G. Cobo, G. Dercon, G. Cadisch, 2009. Nutrient bal- ances in African land use systems across different spatial scales: a review of approaches, challenges and progress.
Agriculture Ecosystems and Environment (in press).
Assessment of anthropogenic and geogenic radionuclides in an undisturbed Slovenian forest soil
P. Jankong1, L. Mabit1, P.C. Martin2, A. Toloza1, R. Padilla-Alvarez2, V. Zupanc3
1Soil Science Unit, Joint FAO/IAEA Division, 2Physics, Chemistry and Instrumentation Laboratory, IAEA
3Department of Agronomy, Biotechnical Faculty, University of Ljubljana, Slovenia
The Challenge
The measurement of natural background radiation and anthropogenic radionuclides in soils has been carried out in many countries for several decades to establish base line data of radiation levels. Through weathering and ero- sive processes, the landscape redistribution of these nu- clides depends on their physicochemical behaviours. So far, the knowledge of radionuclide concentration levels in Slovenia is limited to a few investigations and use of the anthropogenic 137Cs radionuclide has not yet been em- ployed as a soil tracer in Slovenia. Therefore, the pur- poses of this study were: (i) to collect inventory informa- tion of naturally occurring isotopes (40K, 226Ra, 232Th,
235U and 238U) and man-made radionuclides (137Cs) as well as their depth/vertical distribution in soil; (ii) to complete radio-ecological surveys in Slovenia and pro- vide information regarding the external dose-rate based on the depth distributions of the gamma emitters in the soil of the study area; (iii) to undertake a complementary characterization of the chemical composition of the soil, in addition to revealing the major differences in the abun- dance of some elements through the soil depth profile;
and (iv) to establish a reference inventory value of 137Cs fallout in order to prepare a future investigation of 137Cs as a soil tracer in the Slovenian agro-environment.
Experimental design and preliminary results
Twenty soil profiles (0-40 cm) divided into four different increments of 10cm were collected in an undisturbed forest in Pomurje, east Slovenia using a 40 × 30 m grid and a bulk density cylinder to estimate the initial fallout of 137Cs and also to establish the natural level of radioac- tivity in this area, taking into account the activities level of 40K, 226Ra, 232Th, 235U and 238U in soil and their depth distributions. From this information, radium equivalent activity (Raeq), the gamma-absorbed dose rate (D) and annual effective dose rate (E) has been calculated for this forested site. The average mass activity concentrations for depth increments of 137Cs, 40K, 226Ra, 232Th, 235U and
238U are presented in Figure 1, representing a total aver- age areal activity of 7316 ± 2525 Bq m-2, 326745 ± 24572 Bq m-2, 26517 ± 1,720 Bq m-2, 30280 ± 2172 Bq m-2, 4190 ± 290 Bq m-2 and 33504 ± 6412 Bq m-2, respec- tively, for 137Cs, 40K, 226Ra, 232Th, 235U and 238U. These results showed that on average, the top soil mass activity of 40K is 7 to 8 times higher than 137Cs mass activity.
Unlike the constant vertical distribution of other naturally occurring radionuclides (226Ra, 232Th, 235U and 238U), the
40K mass activity increased with depth (Figure 1).
Based on this observation, the radium equivalent activity (167 ± 7 to 187 ± 5 Bq kg-1) and the external gamma dose rate (79 ± 3 to 90 ± 2 nGy h-1) which generates the annual effective dose of natural occurring radioistopes (97 ± 4 to 110 ± 3 µSv a-1) increase with depth of 10% and 11% re- spectively (Table 1). The results obtained from this study
show that the values of Raeq and E are below the limit of 370 Bq kg-1 and 1.0 mSv a-1 recommended by UN- SCEAR (1982) and ICPR (1991), respectively. However, the external gamma dose rate (D) that ranged from 79 ± 3 to 90 ± 2 nGy h-1 is higher than the world average set at 57 nGy h-1 by UNSCEAR (2000).
Table 1. Assessment of radium equivalent activity, external gamma dose rate and annual effective dose in the study area.
External gamma dose rate
D (nGy/h) Annual effective dose
E (µSv/a) Soil depth interval (cm) Radium equivalent activity Raeq (Bg/kg) Naturally occurring radionuclides* 137Cs Naturally oc-
curring ra- dionuclides a
137Cs
0-10 167 ± 7** 79 ± 3 8.2 ± 3.9 97 ± 4 10 ± 5
10-20 168 ± 15 80 ± 7 0.9 ± 0.7 98 ± 9 1.1 ± 0.9
20-30 182 ± 7 87 ± 3 0.12 ±
0.09 107 ± 4 0.15 ± 0.11
30-40 187 ± 5 90 ± 2 0.06 ±
0.03 110 ± 3 0.07 ± 0.04 Figure 1. Vertical distribution of mass activity of 137Cs (a`), 40K (b), 226Ra (c), 232Th (d), 235U (e), and 238U (f). (Data
presented as mean ± SD (n = 20)).
20-30
30-40 10-20 0-10
0 3 6 9 12 15
Activity (Bq/kg dry weight)
Soil depth interval (cm)
U-235
0-10
10-20
30-40 20-30
0 30 60 90 120 150
Activity (Bq/kg dry weight)
Soil depth interval (cm)
U-238 20-30
30-40 10-20 0-10
0 30 60 90 120
Activity (Bq/kg dry weight)
Soil depth interval (cm) Th-232 20-30
30-40 10-20 0-10
0 30 60 90 120
Activity (Bq/kg dry weight)
Soil depth interval (cm) Ra-226
0-10 10-20
30-40 20-30
0 200 400 600 800 1000
Activity (Bq/kg dry weight)
Soil depth interval (cm) K-40
0-10
10-20
30-40 20-30
0 30 60 90 120 150
Activity (Bq/kg dry weight)
Soil depth interval (cm) Cs-137
(c) (d)
(e) (f)
(a) (b)
20-30
30-40 10-20 0-10
0 3 6 9 12 15
Activity (Bq/kg dry weight)
Soil depth interval (cm)
U-235
0-10
10-20
30-40 20-30
0 30 60 90 120 150
Activity (Bq/kg dry weight)
Soil depth interval (cm)
U-238 20-30
30-40 10-20 0-10
0 30 60 90 120
Activity (Bq/kg dry weight)
Soil depth interval (cm) Th-232 20-30
30-40 10-20 0-10
0 30 60 90 120
Activity (Bq/kg dry weight)
Soil depth interval (cm) Ra-226
0-10 10-20
30-40 20-30
0 200 400 600 800 1000
Activity (Bq/kg dry weight)
Soil depth interval (cm) K-40
0-10
10-20
30-40 20-30
0 30 60 90 120 150
Activity (Bq/kg dry weight)
Soil depth interval (cm) Cs-137
(c) (d)
(e) (f)
(a) (b)
Naturally Occurring Radionuclides = 232Th, 40K and 226Ra, ** Mean ± SD, n = 2 To achieve a complete characterization of the soil, the
mass fractions of 51 elements were determined by En- ergy dispersive X-Ray fluorescence (EDXRF) analysis.
The XRF results (Table 2) showed a similar profile shape for the total concentration of K, Th, and U to their radio- active component (40K, 232Th, 235U and 238U). The 30-40 cm soil layer is apparently enriched in Al and Fe. It was also observed that the total K and Mg contents behave in the same way increasing with depth. The specific vertical migration of these elements in soil can be associated with a podzolisation processes that could take place under the
acidic condition of the forest soil. Assessment of the ini- tial 137Cs fallout in undisturbed forest site using nuclear techniques, is a first step to investigate soil redistribution in Slovenian agro-environment. The depth distribution of
137Cs in this undisturbed site showed an exponential de- creased with depth (Figure 1). As expected for a refer- ence site, this will be used for future soil redistribution investigations. 98% of 137Cs is concentrated in the first 20 cm of the soil and the activity in the 30-40 cm soil layer was below detection limit.
.
Table 2. Concentration of some elements in the forest soil obtained by XRF technique.
* Data are presented as mean ± SD, n = 20 Conclusion
The results showed that of the profile activities of the naturally occurring radionuclides only 40K exhibits varia- tion in distribution with depth. As expected in classical undisturbed soils, a typical decreasing exponential distri- bution has been observed for 137Cs. The D value is ap- proximately 30 to 40% more than the global average.
The base-line level of 137Cs in this Slovenian forest soil was established at 7316 ± 2525 Bq m-2 with a coefficient of variation of 34% and this value will be used as an ini- tial inventory for future 137Cs investigation to assess soil erosion and sedimentation processes.
References
Brajnik, D., Korun, M. and Miklavžič, U. (1993). Re- gional distribution of natural and man-made radioactivity in Slovenia. Science of the Total Environment, 130-131, 147–153.
ICRP (1991). ICPR Publication 60. Ann. ICPR (Oxford:
Pergamon Press).
UNSCEAR (2000). Sources and effects of ionising radia- tion. Report of the United Nations Scientific Committee on the Effects of Atomic Radiation to the General As- sembly, United Nations, New York, USA.
UNSCEAR (1982). Ionizing Radiation: Sources and Bio- logical Effects. United Nations, New York.
A first investigation using joint radioactive tracers (137Cs & 210Pbex) to document soil redistribution rates in Morocco
M. Benmansour1, L. Mabit2, A. Nouira1
1 Centre National de l’Energie des Sciences et des Technique Nucléaires, Rabat Morocco, 2 Soil Science Unit, Joint FAO/IAEA Division
The challenge
Despite the severity of land degradation in Morocco, there is only limited data available on the actual magni- tude of soil erosion rates. Since the mid 1990s, few stud- ies have reported the use of the 137Cs approach and the use of excess lead-210 (210Pbex) as a soil tracer has never been tested in Morocco. The objectives of this innovative
137
field using both a classical assessment of soil redistribu- tion rates and spatialization tools.
Experimental design
The site under investigation is a one hectare agricultural field in a semiarid climate, located in Marchouch, 68 km south east of Rabat (Morocco). The soil in the field is a clay soil with a mean slope gradient of 17%. The land use
Concentration (µg/g)* Soil interval
(cm) Si Al Fe K Mg Th U
0-10 (280×10± 8) 3 (72.3×10± 2.1) 3 (30.9×10± 1.2) 3 (16.6×10± 0.4) 3 (9.54×10± 0.78) 3 14.1± 0.7 4.99± 0.77 10-20 (284 ± 4) ×103 (81.7 ± 2.6)
×103 (35.4 ± 1.6)
×103 (18.4 ± 0.4)
×103 (12.0 ± 0.7)
×103 14.5 ± 0.8 4.27 ± 1.20
20-30 (273 ± 4) ×103 (90.5 ± 1.5)
×103 (39.9 ± 1.7)
×103 (20.4 ± 0.2)
×103 (14.6 ± 0.6)
×103 14.6 ± 0.8 3.83 ± 0.70
30-40 (262 ± 7) ×103 (94.2 ± 1.6)
×103 (46.4 ± 2.1)
×103 (20.9 ± 0.2)
×103 (15.8 ± 0.7)
×103 16.6 ± 0.5 5.53 ± 0.83
The initial 137Cs and 210Pb fallout were assessed through 12 core samples collected in an undisturbed pasture lo- cated 3 km from the studied field.
Soil samples were dried, sieved and homogenized prior to measuring 137Cs, 210Pb and 226Ra by γ-spectrometry using a HPGe ‘N Type’ detector (45 % efficiency). Areal ac- tivities of 137Cs and 210Pbex were converted into soil redis- tribution rates using the conversion model MBM 2.
Soil redistribution rates obtained from 137Cs and 210Pb isotopes were analyzed using a geostatistic approach and a classical interpolation concept (inverse distance weight- ing (IDW)). Applying the protocol of Mabit and Bernard (2007), maps of soil redistribution were established and a sediment budget for the whole field was calculated using the GIS Surfer 8.00 package.
Main results
Vertical distribution and inventories of 137Cs and 210Pbex
(i) For the reference site, the vertical distributions asso- ciated with both radionuclides were similar and concentrated in the top 10 cm, with a clear exponen- tial decrease with depth. The 137Cs concentration was highest at the surface (0-3 cm) with a value of 13 q kg-1 while the 210Pbex concentration was 25 Bq kg-1 at the soil surface. The reference inventory val- ues were estimated at 3305 Bq m-2 (n = 12; CV of 30%) and 1445 Bq m-2 (n = 12; CV of 18%) for
210Pbex and 137Cs, respectively.
(ii) For the cultivated site, as a result of tillage, the con- centrations of both radionuclides were almost uni- form throughout the plough layer (~ 16 cm) ranging from 1.9 to 5.9 Bq kg-1 and from 2.2 to 16.7 Bq kg-1 for 137Cs and 210Pbex, respectively. Along the tran- sects, the 137Cs areal activities ranged from 600 to 1900 Bq m-2 and the 210Pbex areal activities ranged from 1700 to 5000 Bq m-2. The uncertainties associ- ated with 210Pbex are generally higher than those cor- responding to the 137Cs due to the low intensity of
210Pb gamma rays and the background contribution in this energy range.
Classical assessment of soil redistribution rates as derived from 137Cs and 210Pbex
From 137Cs measurements and the use of the conversion Mass Balance Model II (MBM II), the erosion rates (over
~50 years) in the field study ranged from 4 to 30 t ha-1 a-1. Eroded zones in the upslope part of the field represented 82% of the total area, while soil deposition occurred in the lower slope position on the remaining 18% of the area. From 210Pbex data, the erosion rates (over ~ 100 years) ranged from 8 to 27 t ha-1 a-1. The eroded and de- positional areas represent 84% and 16%, respectively.
Using the average values of transects, the results pro- vided by 137Cs and 210Pbex techniques were comparable (Table 1).
Table 1. Sediment budget and soil redistribution assess- ment from 137Csand 210Pbex using a simplified approach (Benmansour et al., 2010).
Additional soil redistribution evaluation using spatialization approach
Experimental variograms for soil redistribution rates cal- culated from the data provided by the 137Cs and 210Pbex
results were fitted. Following the optimization of variographic parameters and cross-validation analysis, the geostatistical study of the data reported a very weak autocorrelation with a high nugget effect, a non signifi- cant coefficient of correlation (r2) < 0.4 and a low ratio scale to sill close to 0.4. As suggested by Mabit and Ber- nard (2007) in the case of weak or absent spatial struc- ture, the use of classical methods of interpolation is rec- ommended. Therefore, a simple spatialization of the data using IDW2 was used to map soil redistribution based on
137Cs and 210Pbex results. Contour maps and soil redistri- bution budgets were established using the IDW2 (Figure 1 and Table 2). Similar results regarding soil redistribu- tion magnitude were obtained for 137Cs and 210Pbex. The high sediment delivery ratio (SDR), corresponding to the net/gross erosion ratio rate which was obtained using
137Cs and 210Pbex approaches showed that most of the mo- bilized sediment was moved out of the field.
This is a logical result based on the fact that soil cultiva- tion is conducted along the main slope direction, on a slope that reaches 17%. This high SDR also reflects the fact that using 137Cs and 210Pbex techniques the eroded area represents 93 to 96% of the field surface and the deposition area covers only 7 to 4%.
Table 2. Sediment budget and soil redistribution assess- ment for (A) 137Cs and (B) 210Pbex using IDW2 interpola- tion.
Soil redistribution magnitude 137Cs 210Pbex
Mean erosion (t ha-1 a-1) 17.9 15.0 Mean deposition (t ha-1 a-1) 6.3 4.1 Gross erosion (t ha-1 a-1) 15.4 12.9 Gross deposition (t ha-1 a-1) 1.2 0.8 Net erosion (t ha-1 a-1) 14.3 12.1 Sediment delivery ratio (%) 92% 93%
Soil redistribution magnitude A B Mean erosion (t ha-1 a-1) 13.1 11 Mean deposition (t ha-1 a-1) 3.5 3 Gross erosion (t ha-1 a-1) 11 10.5 Gross deposition (t ha-1 a-1) 0.3 0.1 Net erosion (t ha-1 a-1) 11.7 10
Sediment delivery ratio (%) 94 95
Conclusion
This study illustrates the potential benefit of the com- bined use of fallout 137Cs and 210Pbex and GIS to estimate long-term soil redistribution rates and to establish sedi- ment budget of agricultural fields in Morocco. Under the experimental condition, the soil redistribution rates gen- erated by the 137Cs and 210Pbex techniques using the sim- plified approach (MBM2 without interpolation of the data set) and the spatialization of the data were in the same order of magnitude. The relatively high erosion and low deposition rates obtained for this field can be attributed to the steep slope (slope that can reaches 17%) and to the soil cultivation (tillage) in the direction of the slope.
References
Benmansour, M., Nouira, A., Bouksirat, H., Duchemin, M., El Oumri, M., Mossadek, R., Benkdad, A., Ibn Ma- jah, M. (2010). Estimates of long and short-term rates of soil erosion using 137Cs, 210Pbex and 7Be measurements:
case study of one agricultural field in semi-arid west Mo- rocco. IAEA Publication, IAEA-TECDOC (In press).
Mabit, L., Bernard, C. (2007). Assessment of spatial dis- tribution of Fallout RadioNuclides through geostatistics concept. Journal of Environmental Radioactivity, 97(2- 3), 206–219.
Figure 1. Maps of soil redistribution for (A) 137Cs and (B) 210Pbex using IDW2 (t ha-1 a-1).
Can yields and water use efficiency be improved by shading? Isotopes can help solve the question.
By Shabtai (Shep) Cohen
Institute of Soil, Water and Environmental Sciences, Volcanic Centre,
Agricultural Research Organization, Ministry of Agriculture and Rural Development, Bet Dagan, Israel
Greenhouses produce is often of much better quality than field grown produce, and often growers in indoor inten- sive agricultural production can produce higher yields than their colleagues outdoors. But if light powers photo- synthesis, or plant productivity, shouldn’t the reduction in radiation incurred in the greenhouse decrease productiv- ity? In Holland, a leader in greenhouse agriculture, grow- ers clean cladding continuously just for that reason, in order to get the maximum light.
In semi-arid climates solar radiation levels far exceed those in Europe and water, not light, is often the limiting factor for crop production. In this case solar radiation heats the crop, causing water stress which forces the plants to decrease their water loss and productivity. But if the plant is well irrigated should it suffer from excess sunlight? It turns out that in many cases, especially in tree crops, even a well irrigated plant will show signs of water stress at high radiation levels in arid climates. This is the idea behind this IAEA-partially funded research project which investigated the plant’s physiology, water use and yields for different shading treatments in Israel’s semi- arid, high solar radiation, summer climate. Carbon iso- tope ratios served as a tracer to track the physiological changes in the leaves that accompany the changes in wa- ter use and productivity.
Productivity of citrus trees, which have well developed foliage on a limited hydraulic frame, increases signifi- cantly due to shading. This increase was always accom- panied by a decrease in the ratio of C13 to C12, indicat- ing that the small pores on the leaves, called stomata, were more open in the shade. Tree and crop water use was similar to that outside because of this response.
Overall water use efficiency thus increased in the shade.
Similar, results were obtained in shading trials with apple trees and banana plants.
Peppers grown under screens in arid southern Israel are irrigated with poor quality water and often suffer from accumulations of salinity in the soil. A trial with different irrigation strategies showed that when the plant suffered from high salinity the pores also closed and the carbon isotope ratios showed clear and unambiguous indications of this.
These results show the usefulness of carbon isotope test- ing for finding differences in water relations of plants in shading, irrigation and other treatments. We found that processing of leaves for isotopic analysis is easy com- pared to the field measurements needed for determining daily courses of leaf physiology and yields. If properly mixed, leaf samples from several trees can be combined and the variance in the isotopic ratios obtained from dif- ferent plots will be very small.
Shading effects on yield and water use efficiency by green peppers (a) and bananas (b)
This means that with three or four samples from each treatment we get a very precise isotopic signal, and since most labs charge approximately $10 per analysis the analysis is relatively cheap. We have therefore begun to include carbon isotope analyses in all our irrigation trials.
Following is a case in point. In this year’s irrigation trials in a persimmon orchard a malfunction in the irrigation system at the beginning of the season led to a full 24 hours of irrigation (and a lot of extra water) in our ex- perimental plots. This may invalidate the full year of re- sults, which means significant financial cost due to the need for another year of the trial. Last year's isotope re- sults showed the treatment differences clearly and this year’s results should give us an indication if the treat- ments were effective this year, in which case we can trust the yield results.
Another case is our current study of the use of cytokinins in the irrigation water to influence water relations. The concentrations we used were recommended by a chemi- cal importer and used by the farmers without proper ex- perimentation. Our experiments showed that these con- centrations had no significant impact on water relations or yield in normal and deficit irrigation treatments. Sure enough, the carbon isotope signal showed clear signals for irrigation levels and no influence of cytokinin.
In conclusion, this project helped to establish that the re- lationship between δC13 and shading is consistent. The excellent resolution and precision of the measurements obtained with the field collection techniques used and the lab that did the processing indicate that this measure is a relatively cheap and accurate way to monitor differences in shading intensity and irrigation level.
SWMCN Seminar Series
FAO/IAEA Seminar
Biochar carbon negative Amazonian trea- sure - ‘Cool Farming!’
By Rebecca Hood-Nowotny
SWMCN Section, Joint FAO/IAEA Division
Rebecca Hood joined the SWMCN Subprogramme in January 2009 as a consultant. She currently works on de- veloping methods for measuring greenhouse gas emis- sions and carbon sequestration
ABSTRACT
Carbon mitigation strategies and mechanisms have been globally implemented in an attempt to prevent catastro- phic climate change. Kyoto targets require reductions in greenhouse gas emissions and increases in carbon seques- tration. Although a number of carbon neutral technolo- gies have been adopted such as bio-fuel and alternative energies, these currently fail to meet global requirements.
An innovative and rediscovered carbon negative strategy is biochar production and soil incorporation. Biochar production is a variant of bio-energy production, which yields energy and a biochar (charcoal) product which when added to soil locks away carbon for millennia. Bio- char incorporation into soil has also been shown to dou- ble crop yields and decrease greenhouse gas emissions in low fertility soils. Scenario analysis has suggested that biochar sequestration could offset up to two thirds of the global annual net CO2 accumulation (15 Pg C a-1). Ironi- cally ancient Amazonian people knew of the benefits of biochar, cultivating highly fertile Terra Pretas (Black Soils) by incorporation of char into their soils (Lehmann 2007).
Biochar is formed by partial combustion or pyrolysis of plant derived biomass or waste- stream products, yielding a continuum of black carbon (BC) compounds. It is bio- char’s aromatic-macromolecular structure that renders it more recalcitrant to microbial decomposition than un- charred organic matter and makes it a potential long-term carbon sink. Evidence from ancient Terra Preta and car- bon dating suggest that biochar has a mean residence time in the range of 1000-10 000 years. To put this in perspective, when un-charred organic matter is added to the soil it is mineralized within months with a small por- tion of the carbon stabilized for hundreds of years. An- other problem is that the application of large amounts of un-charred carbon to the soil can cause immobilisation of valuable inorganic nitrogen, leading to reductions in crop yield due to nitrogen deficiency. Biochar addition to soil does not cause significant nitrogen immobilisation be- cause it is not assimilated by the soil microbial biomass.
Biochar addition has been shown to improve soil fertility, substantially increasing biomass production in tropical soils (Lehmann 2007, Steiner et al., 2006) probably due to the associated increase in soil cation exchange capacity (Liang et al., 2006). Preliminary greenhouse experiment results suggest that the presence of biochar may reduce emissions of two potent greenhouse gases, nitrous oxide and methane (Rondon 2005).
The benefits of adding Biochar to low cation exchange capacity tropical soils are clear from the success of the fertile Terra Pretas and recent experiments (Glaser et al., 2002, Steiner et al., 2006). However for Biochar applica- tion to become an acceptable routine agronomic practice and have a major impact on global carbon budgets, a more detailed scientific understanding of the conse- quences of Biochar addition to soil is required.
Stable isotopes have and will play a key role in unravel- ling the complex chemical and physical interactions and benefits of Biochar. Stable isotope techniques allow the direct tracing of the pathways and processes that account for the environmental and nutrient benefits of Biochar.
For example using 15N labelled fertilizers, it is possible to directly trace the fate of applied nitrogen and calculate ni- trogen use efficiency on addition of fertilizer and Bio- char. It is also possible to study the effect of Biochar ad- dition on the fundamental soil processes of nitrogen min- eralization and nitrification using 15N isotope dilution techniques. In addition it is possible to study the mecha- nisms associated with the reduction in potent greenhouse gas emissions such as nitrous oxide. Carbon isotopes en- able us to unravel the carbon side of the story; recent work using carbon isotopes has shown that the carbon added as Biochar is highly resistant to soil microbial at- tack and therefore acts as an extremely long term carbon sink in soils. Using the isotopes of hydrogen and oxygen it will also be possible to determine the impact of Biochar on soil-water interactions.
The beauty of isotopic techniques is that they enable us to study soil processes in policy relevant time frames over seasons rather than decades, which means policy makers are armed with sufficient knowledge to make informed decisions about national and international carbon poli- cies, which will ultimately determine the future of the planet.
AquaCrop for Agricultural Water Management
By Lee Heng
SWMCN Section, Joint FAO/IAEA Division
Lee Heng joined the Agency in June 2007 in the Soil and Water & Crop Nutrition (SWMCN) Section as a soil sci- entist. She currently provides technical support for both CRPs and TCPs in the area of soil-water-nutrient-crop in- teraction.
ABSTRACT
AquaCrop is a crop water productivity model developed by FAO. It resulted from the revision and update of the FAO Irrigation and Drainage Paper No. 33 ‘Yield Re- sponse to Water’ (Doorenbos and Kassam, 1979), for es- timating the yield response to water.
AquaCrop is particularly suited to addressing conditions where water is a key limiting factor in crop production. It is a water-driven model, i.e. crop growth and production are driven by the amount of water transpired (Tr) using a conservative parameter—biomass water use efficiency (or water productivity), normalized for atmospheric evaporative demand and carbon dioxide concentration.
This normalization makes AquaCrop applicable to di- verse locations and seasons, with the capability of pre- dicting crop responses under future climate scenarios.
AquaCrop attempts to balance accuracy, simplicity, and robustness. It uses a relatively small number of parame- ters and input variables requiring simple methods for their determination.
Some of the applications of AquaCrop include: (i) assess- ing water-limited, attainable crop yields at a given geo- graphical location; (ii) comparing attainable yields against actual yields of a field, farm, or region, to identify the yield gap and the constraints limiting crop production - benchmarking tool; and (iii) developing irrigation schedules for maximum production for different climate scenarios.
During this presentation, case studies using maize and soybean crops and economic optimization under deficit irrigation in cotton production in Spain will be presented.
Demonstration on the use of the software will also be given.
Non FAO/IAEA Seminar
Use of Fallout Radionuclides at Basel Uni- versity, 14
thOctober 2009, Basel, Switzer- land
By Lionel Mabit (Soil Science Unit FAO/IAEA Agricul- ture and Biotechnology Laboratory)
Lionel Mabit was invited as the guest speaker for the seminar course series Kolloquien der Geographie – HS 2009 by the Department of Environmental Sciences, In- stitute of Environmental Geosciences, Basel University (Switzerland).
The main aim of his seminar entitled ‘The use of fallout radionuclides (FRNs) to assess erosion and sedimenta- tion processes from field to basin scale’ was to highlight various tools and protocols to upscale the use of FRNs to the watershed and basin scale.
After an introduction on soil degradation and a brief re- view of the advantages and limitations of using 137Cs,
210Pb and 7Be as soil tracers, three examples were pre- sented to illustrate FRNs investigations for establishing soil redistribution from field to basin scale.
The first example looked at a study carried out in Quebec, Canada in a small 2.16 ha field. A full se- diment budget (gross erosion, net erosion and sedi- ment delivery ratio) was presented using 137Cs, geo- statistics and classical interpolation methodologies.
A simple protocol was presented taking into account the spatial autocorrelation of the data set (caesium activity and soil movement rates).
The second example, a study implemented in a 180 ha French watershed using 137Cs and geostatistics approaches illustrated how spatialization tools allow the establishment of soil redistribution and a sedi- ment budget at the watershed scale.
The third example was a case study highlighting the support provided by the geographical information system (GIS) in the use of 137Cs to evaluate a full sediment budget of the Boyer River watershed, a large Canadian basin of 217 km2. GIS was used to build an oriented sampling strategy to select repre- sentative agricultural fields in the basin for analysis using 137Cs methodology, taking into account the land use and soil-slope combinations divided into isosectors. The result of the sediment production of the different isosectors and a full sediment produc- tion at the basin scale was presented and risk areas identified.
This presentation also gave a selective overview of cur- rent and previous research activities of the Soil Science Unit (SSU) of the Joint FAO/IAEADivision of Nuclear Techniques in Food and Agriculture.
Technical Cooperation Projects
Operational Projects and Technical Officers responsible for implementation
Project Number Title Technical Officer
AFG5003 Sustainable Increase in Crop Production in Afghanistan Nguyen, Minh-Long in collabora- tion with the Plant Breeding and Genetics Section
ALG5021 Optimizing Irrigation Systems and Surface Water Man-
agement Heng, Lee Kheng
ALG5022 Nuclear Techniques for Sustainable Use of Saline
Groundwater and Wastelands for Plant Production Heng, Lee Kheng ANG5005 Effect of Biofertilizer and Inorganic Fertilizer Uses on the
Growth and Yield of Maize and Bean in Ferralitic Soils of Huambo
Hardarson, Gudni
BEN5005 Improving Maize and Yam-Based Cropping Systems and
Soil Fertility Adu-Gyamfi, Joseph Jackson
BGD5026 Increasing Agricultural Production in the Coastal Area
through Improved Crop, Water and Soil Management Adu-Gyamfi, Joseph Jackson in collaboration with the Plant Breed- ing and Genetics Section
BKF5007 Improving Voandzou and Sesame Based Cropping Systems Through the Use of Integrated Isotopic and Nuclear Tech- niques
Sakadevan, Karuppan in collabora- tion with the Plant Breeding and Genetics Section
CHI5048 Integrated Watershed Management for the Sustainability of
Agricultural Lands Mabit, Lionel in collaboration with
the Food and Environmental Pro- tection Section
CMR5016 Development of N and P fertilizer management for Sus- tainable Intensification of Agricultural Production in Cam- eroon
Heng, Lee Kheng
ECU5024 Improving Productivity of the African Palm through Better
Fertilization and Water Management Practices Dercon, Gerd ECU5026 Improving the Efficiency of Irrigation in the Rio Chota
Sub-Basin Sakadevan, Karuppan
ELS8009 Study of Sedimentation in the Reservoirs of the Four CEL
Hydroelectric Power Stations Dercon, Gerd
ERI5004 Improving Crop Productivity and Combating Desertifica-
tion Adu-Gyamfi, Joseph Jackson/
Nguyen, Minh-Long in collabora- tion with the Plant Breeding and Genetics Section
HAI5003 Enhancing Crop Productivity through the Application of
Isotope Nuclear Techniques Sakadevan, Karuppan in collabora-
tion with the Food and Environ- mental Protection Section INS5035 Application of Nuclear Techniques for Screening and Im-
proving Cash Crop Plants in Coastal Saline Lands Dercon, Gerd in collaboration with the Plant Breeding and Genetics Section
INS5037 Applying Nuclear Techniques for Screening and Improving
Cash Crop Plants in Coastal Saline Lands Sakadevan, Karuppan in collabora- tion with the Plant Breeding and Genetics Section
IRQ5017 Optimization of Land Productivity through the Application
of Nuclear Techniques and Combined Technologies Nguyen, Minh-Long in collabora- tion with the Plant Breeding and Genetics Section
IVC5031 Improving Plantain and Cassava Yields through the Use of
Legume Cover Crops Hardarson, Gudni
KEN5030 Assessing Nutrient and Moisture Use in Major Cropping
Systems Heng, Lee Kheng
Project Number Title Technical Officer MAG5014 Use of Environmental Radioisotopes for the Assessment of
Soil Erosion and Sedimentation and for Supporting Land Management in the Province of Antananarivo, Madagascar
Mabit, Lionel
MAG5015 Optimization of Phosphate Fertilization of Ferralsols (clas- sically deeply weathered red or yellow soils found in hu- mid east Madagascar) in the Highland Areas of Madagas- car
Nguyen, Minh-Long Dercon, Gerd
MAR5017 Investigating the N Dynamics in the Crop-Soil System of a
Multiple Cropping System to Optimize Fertilizer Use Nguyen, Minh-Long MLI5021 Sustainable Intensification and Diversification of Sorghum
Production Systems in the Southern Zone of Mali, Phase-1 Heng, Lee Kheng MLI5022 Assessment of Erosion and Sedimentation in the Niger Wa-
tershed with the Use of Radioisotopes, Phase-1 Mabit, Lionel MLW4002 Supporting Capacity Building in Nuclear Science and
Technology Heng, Lee Kheng
MON5015 Implementation of the Fallout Radionuclide Technique for
Erosion Measurement Dercon, Gerd
MOZ5003 Sustaining the Management of Soil Fertility Dercon, Gerd NAM5009 Using Mutation Breeding and Integrated Soil Plant Man-
agement Techniques to Develop Sustainable, High Yield- ing and Drought Resistant Crops
Heng, Lee Kheng in collaboration with the Plant Breeding and Genet- ics Section
NIC8012 Applying Nuclear Techniques for the Development of a
Management Plan for the Watershed of the Great Lakes Dercon, Gerd QAT5002 Developing Biosaline Agriculture in Salt-affected Areas in
Qatar Nguyen, Minh-Long in collabora-
tion with the Plant Breeding and Genetics Section
RAF5058 Enhancing the Productivity of High Value Crops and In-
come Generation with Small-Scale Irrigation Technologies Heng, Lee Kheng RAS5043 Sustainable Land Use and Management Strategies for Con-
trolling Soil Erosion and Improving Soil and Water Quality (RCA)
Dercon, Gerd
RLA5051 Using Environmental Radionuclides as Indicators of Land Degradation in Latin American, Caribbean and Antarctic Ecosystems (ARCAL C)
Dercon, Gerd
Voigt, Gabriele Margarete RLA5052 Improving Soil Fertility and Crop Management for Sus-
tainable Food Security and Enhanced Income of Resource- Poor Farmers (ARCAL CI)
Sakadevan, Karuppan
RLA5053 Implementing a Diagnosis System to Assess the Impact of Pesticide Contamination in Food and Environmental Com- partments at a Catchment Scale in the Latin American and Caribbean (LAC) Region (ARCAL CII)
Dercon, Gerd in collaboration with the Food and Environmental Pro- tection Section
SAU5003 Improving Fertilization under Saline Conditions for Sus-
tainable Crop Production Nguyen, Minh-Long in collabora-
tion with the Plant Breeding and Genetics Section
SEN5030 Integrated Approach to Develop Sustainable Agriculture in
Senegal Dercon, Gerd in collaboration with
the Plant Breeding and Genetics Section
SEY5004 Developing Improved Nutrient Management Practices Us- ing Nuclear and Related Techniques for Enhancing Sus- tainable Agricultural Productivity
Heng, Lee Kheng
SIL5008 Contribution of Nitrogen Fixing Legumes to Soil Fertility
in Rice-based Cropping Systems Hardarson, Gudni
SIL5012 Managing Irrigation Water for a Dry Season Sor- Adu-Gyamfi, Joseph Jackson
Project Number Title Technical Officer SRL5038 Application of Isotope Techniques for Soil Erosion Studies Dercon, Gerd
SRL5040 Study on Nitrogen Balance in Coconut-Based Agroforestry
Systems Using Nitrogen-15 Isotope Dilution Technique Hardarson, Gudni SUD5030 Increasing Productivity of Selected Crops Using Nuclear
Related Techniques Adu-Gyamfi, Joseph Jackson in
collaboration with the Plant Breed- ing and Genetics Section
TAD5002 Assessment of Soil Erosion and Sedimentation for Land
Use Dercon, Gerd
TAD5005 Developing Soil Conservation Strategies for Improved Soil
Health Dercon, Gerd
TUR5024 Improving Crop Productivity through Nuclear and Related
Techniques Nguyen, Minh-Long
UGA5029 Developing Soil Conservation Strategies Dercon, Gerd ZAI5017 Use of Isotope Techniques in Relation with the Nitrogen
Dynamic and the Quality of Organic Plant Material in Ag- ricultural Soil Management
Nguyen, Minh-Long/Dercon, Gerd
ZAM5026 Improving Crop Varieties Through Use of Nuclear Tech-
niques Heng, Lee Kheng in collaboration
with the Plant Breeding and Genet- ics Section
ZIM5011 Combating Desertification in Agricultural Drylands Heng, Lee Kheng ZIM5014 Developing and Promoting Strategies for Improved Crop
Production Heng, Lee Kheng
